1. Technical Field
The present invention relates generally to rupture disks used to actuate tools used in subterranean wells and, specifically relates to a rupture disk that can be ruptured upon receipt of a predetermined triggering signal from a remote source. The triggering signal can be an acoustic pressure pulse, an electromagnetic signal, a seismic signal, or from any other suitable source.
2. Description of the Related Art
Many downhole tools are dynamic. In other words, their movement or configuration can be altered once the tool has been lowered into the well as part of a tool string. Changing the configuration of a downhole tool is typically accomplished through the use of control lines that supply hydraulic pressure to the tool. The hydraulic pressure, when applied, can be used to push elements within the tool to specific locations or to perform specific functions.
A downhole tool has a specific function and typically must be actuated when it is adjacent to a specific formation strata. However, the use of control lines to actuate the tool implicates a number of additional design problems. For example, as the length of the control line increases, so does the hydraulic head experienced on the tool simply from the weight of the hydraulic fluid in the line. Further, the use of control lines increases the cost of the job and the risk of equipment failure.
Rupture disks offer another method of actuating downhole tools. A rupture disk is a plug used to block ports in the tool. Prior art rupture disks are designed to fail when subjected to a predetermined pressure. Once the disk fails, the port is exposed to pressurized fluid from outside the tool, which can flood compartments within the tool. The fluid pressure is then used to actuate the tool, instead of control line pressure. The pressure of the fluid is a function of the well depth. In other words, the increase in pressure is proportional to the depth of the well. The depth of the strata of interest is generally known. Therefore, the rupture disk chosen for a particular tool is sized to fail at the pressure associated with the depth of the specific strata.
FIGS. 1 to 5 illustrate the use of a rupture disk 12 with a prior art downhole valve 10. The valve 10 has a blocking member 16 that is generally spherical. The blocking member 16 has a central passage 18 that will allow the flow of fluid through the valve. The blocking member can also be rotated by linkage 20 to block the flow of fluid. The rupture disk is used to block port 14. The rupture disk is connected to the outer frame of the valve 10 across the port 14 with threads 12b. When the valve is lowered to a sufficient depth, the annulus pressure will rupture the disk, specifically, the pressure will rupture a centrally located rupture surface 12a, best shown in FIG. 5. Pressurized annulus fluid will then flood into chamber 22 and act against surface 24 of sliding member 26. As chamber 22 fills with fluid, the sliding member 26 will be forced downward within the valve 10. The sliding member 26 is coupled to the blocking member 16 by linkage 20 so that the downward motion of the sliding member 26 rotates the blocking member 16 into a blocking position. This tool configured for use with a rupture disk is susceptible to the same errors as plague all prior art rupture disks, an inability to precisely control the depth of actuation.
A need exists for a system of controlling the precise depth at which a rupture disk ruptures. Such a system would allow a tool to be placed at a correct depth before actuation. Further, such a system would include both an improved method for controlling the rupture event as well as an improved rupture disk apparatus.
The present invention provides both an improved method of actuating a downhole tool with a rupture disk as well as an improved rupture disk apparatus. The improved rupture disk includes a casing with a central flow passage and a rupture portion across the flow passage. The rupture disk also has a destructive material nested adjacent to the rupture portion. The destructive material can be either an explosive or a corrosive chemical. A rupture event can be initiated by the transmission of an acoustic signal down the fluid column in the well""s annulus. The transmission could also be transmitted down the fluid column within the tool string. The signal is received by a receiver that generates a triggering signal that detonates the explosive destroying the rupture element. If a corrosive is released instead, it may simply weaken the rupture portion enough that the annulus pressure will burst the rupture portion.
The receiver can be a simple piezoelectric crystal with a range of vibrational frequencies. When a suitable vibrational acoustic signal is received by the crystal, it will produce a current which can be used to trigger the rupture event. This embodiment likewise would allow for the sequential firing of multiple ruptured disks. In one embodiment, several crystals can be coupled to separate rupture disks, wherein each crystal has a different resonant frequency. This allows separate addressing of various rupture disks and allow for the sequential firing of multiple rupture disks. Alternatively, the receiver can be a battery powered acoustic receiver coupled to a microprocessor. In this embodiment the microprocessor can be programmed to recognize many different acoustical signals and address any of the multiple number of ruptured disks with triggering signals. The method and apparatus is an improvement over the prior art in that the use of an acoustic signal to initiate the rupture event enables the user to ensure that the downhole tool has been properly located before actuation.